1. Field of the Invention
The invention relates to an improved method of, and apparatus for, drawing wire, in particular ferrous wire, which is an extension of the techniques described in the specifications of U.S. Pat. Nos. 4,345,451 and 4,464,922.
The term "wire" as used in this specification is not intended to be limited to material of circular cross-section since the invention extends to any ductile metallic material of solid cross-section irrespective of its cross-sectional shape.
2. Discussion of Prior Art
In the above-mentioned patent specifications, wire-drawing methods are disclosed which involve the use of a driven wire-engaging drawing wheel to generate the necessary drafting tension for drawing wire through a die, the wire being wrapped around the wheel for less than one complete turn or for a few turns plus less than one complete turn and being directly contacted by a liquid coolant after leaving the die and while wrapped around the drawing wheel.
The methods described in the above-mentioned patent specifications have given excellent results, particularly with regard to the properties of the drawn wire (e.g. ductility as measured by conventional tensile, torsion and/or bend tests) and it is felt these improved properties are, in part, a consequence of an overcoming of the cooling restrictions typical with conventional machines even when the reduction of cross-sectional area of the wire effected at the sizing orifice in a die in a patented apparatus is considerably in excess of what is customary with conventional machines. However when employing these large reductions of cross-sectional area (which can exceed some 40% per die) it has been found that die wear can increase to an unacceptable degree. Nevertheless, apart from this disadvantage of reduced die life, very satisfactory wire can be produced with such large area reductions, and operating the method in this way does not result in wire breakage due to the very high drafting tensions required.
Clearly one solution to the problem of excessive die wear is to increase the number of drawing stages to obtain the desired overall reduction of cross-sectional area with a smaller reduction of area per stage. This is a solution which significantly increases the cost of a machine since the electrical equipment to drive and control the speed of each drawing wheel is expensive. Furthermore increasing the number of drawing stages requires a larger floor area to accommodate the machine.